"The soldiers were among 60 to 100 members of a Special Forces Operation team that trains Pakistan's paramilitary Frontier Corps in counter-insurgency techniques, including intelligence gathering and development assistance.
"The Special Forces training, underway for the last 18 months, has been acknowledged gingerly by both the Americans and the Pakistanis but has been deliberately kept low-key so as not to trespass onto Pakistani sensitivities about sovereignty, and not to further inflame high anti-American sentiment.
"Even though Pakistan is termed an ally by the United States, Pakistan has not allowed American combat forces to operate here.
"To disguise themselves, , the U.S. soldiers were dressed in traditional Pakistani garb of baggy trousers and long tunics, according to a Frontier Corps officer.
"Their armoured vehicle was equipped with electronic jammers sufficient to detect remote-controlled devices and mines, the officer said. Vehicles driven by the Frontier Corps were placed in front and back of the Americans as protection, he said.
"Still, the bomber was able to penetrate their cordon."
Reuters quotes Ahmed Rashid, a Pakistani analyst and expert on militant, as saying of the revelation: "It will only convince the public, even moderate Pakistanis who are anti-Taliban, that the government is doing nothing expect lying to them, and the military (is) for that matter. It will be a big blow for public morale."
The report added: "First television channels said the dead foreigners were journalists, then officials said they were aid workers. Only later did the Pakistani military and the U.S. embassy say they were American soldiers."
Pakistan's foreign ministry spokesman said the U.S. soldiers were invited by the Pakistani paramilitary Frontier Corps to attend the inauguration of a U.S.-funded girls' school.